This invention relates broadly to position monitoring apparatus and, in particular, monitoring apparatus having a magnetic sensing system which system serves simultaneously as part of the operative components of a controllable electromagnetic actuator.
Many kinds of position monitoring devices are well-known. Typically, these indicate the relative position of a moving object or provide for accurate position control of relatively movable objects by translating motion of the moving object into a feedback signal for closed-loop control of the moving object. It is also well-known to use magnetic sensing systems for such devices. A rather common magnetic monitoring system utilizes the Hall effect. To take advantage of the Hall effect, use is made of a Hall probe or generator, whose output voltage is proportional to the product of the current passing through it and the magnetic field perpendicular to it.
An example of a position monitoring device utilizing a magnetic sensor of the Hall type is disclosed in U.S. Pat. No. 3,199,630. As described, a Hall voltage generator is mounted on one of two relatively movable members so as to be in a fixed spaced relationship to a single permanent magnet carried by one of these members. When the Hall generator is used to sense or indicate a preselected position, the Hall voltage reaches a predetermined maximum value so as to indicate that the permanent magnet is aligned with the Hall generator. Also disclosed is an arrangement, wherein the magnetic sensing device is used in a controller. In such arrangement, the Hall generator has its Hall voltage at zero when the generator is positioned over the middle of a flat magnet. Displacement of the probe in a given direction from a location before the middle to a position beyond the middle will cause the voltage polarity to change and for a very limited displacement this change in voltage will be linear. The approach used for positioning relies upon the Hall probe reaching a null position for indicating accurate positioning. U.S. Pat. No. 3,344,347 is exemplary of another position monitoring system using a magnetic sensing device of the Hall type. This approach teaches the use of a Hall probe for monitoring an arcuate magnetic field produced by a single conductor. Although the monitoring is disclosed as useful for control purposes because of a linearity in the Hall voltage, such linearity is limited by the size of the conductor.
Besides the foregoing drawbacks, none of the known position monitoring devices of the Hall type form an integral part of a drive system for driving relatively movable members.